Day 7

l0s · l0s · commit 6ec140fc5b9f · 2021-12-06T21:24:10.000-08:00
diff --git a/src/test/java/com/macasaet/Day07.java b/src/test/java/com/macasaet/Day07.java
@@ -0,0 +1,113 @@
+package com.macasaet;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * --- Day 7: The Treachery of Whales ---
+ */
+public class Day07 {
+
+    protected Stream<String> getInput() {
+        return StreamSupport
+                .stream(new LineSpliterator("day-07.txt"),
+                        false);
+    }
+
+    /**
+     * @return the horizontal position of each crab submarine in the swarm
+     */
+    protected List<Integer> getCrabPositions() {
+        final var list = getInput().collect(Collectors.toList());
+        final var line = list.get(0);
+        return Arrays.stream(line.split(","))
+                .mapToInt(Integer::parseInt)
+                .collect(ArrayList::new, List::add, List::addAll);
+    }
+
+    /**
+     * Assuming a constant fuel consumption rate, calculate the fuel required for the swarm to reach <em>alignmentPoint</em>.
+     *
+     * @param positions      the starting position of each crab submarine
+     * @param alignmentPoint a potential point for the crabs to gather in order to blast a hole in the ocean floor
+     * @return the fuel required to reach the alignment point
+     */
+    protected int calculateConstantFuel(final Iterable<? extends Integer> positions, final int alignmentPoint) {
+        int sum = 0;
+        for (final var position : positions) {
+            sum += Math.abs(alignmentPoint - position);
+        }
+        return sum;
+    }
+
+    /**
+     * Calculate the fuel required for the swarm to reach <em>alignmentPoint</em>
+     *
+     * @param positions      the starting position for each crab submarine
+     * @param alignmentPoint a potential point for the crabs to gather in order to blast a hole in the ocean floor
+     * @return the fuel required to reach the alignment point
+     */
+    protected int calculateFuel(final Iterable<? extends Integer> positions, final int alignmentPoint) {
+        int sum = 0;
+        for (final var position : positions) {
+            sum += calculateFuel(position, alignmentPoint);
+        }
+        return sum;
+    }
+
+    /**
+     * Calculate the fuel required for a single crab submarine to travel from one horizontal position to the next.
+     *
+     * @param start the starting position (inclusive)
+     * @param end   the ending position (inclusive)
+     * @return the amount of fuel consumed in the journey
+     */
+    protected int calculateFuel(final int start, final int end) {
+        final int target = Math.abs(end - start);
+        int sum = 0;
+        for (int i = target; --i >= 0; ) {
+            sum += i + 1;
+        }
+        return sum;
+    }
+
+    @Test
+    public final void part1() {
+        int min = Integer.MAX_VALUE;
+        int max = Integer.MIN_VALUE;
+        final var positions = getCrabPositions();
+        for (final var position : positions) {
+            min = Math.min(min, position);
+            max = Math.max(max, position);
+        }
+        final int result = IntStream.range(min, max)
+                .map(alignmentPoint -> calculateConstantFuel(positions, alignmentPoint))
+                .min()
+                .getAsInt();
+        System.out.println("Part 1: " + result);
+    }
+
+    @Test
+    public final void part2() {
+        int min = Integer.MAX_VALUE;
+        int max = Integer.MIN_VALUE;
+        final var positions = getCrabPositions();
+        for (final var position : positions) {
+            min = Math.min(min, position);
+            max = Math.max(max, position);
+        }
+        final int result = IntStream.range(min, max)
+                .map(alignmentPoint -> calculateFuel(positions, alignmentPoint))
+                .min()
+                .getAsInt();
+        System.out.println("Part 2: " + result);
+    }
+
+}
diff --git a/src/test/resources/sample/day-07.txt b/src/test/resources/sample/day-07.txt
@@ -0,0 +1 @@
+16,1,2,0,4,2,7,1,2,14
